The Ap-1 transcriptional complex is an important regulator of gene expression. It is clear that this complex mediates the expression of many genes and also mediates in part the biologic effects of the class of tumor promoters, phorbol esters. Since cJun is a major component of this complex, we have undertaken to isolate and characterize dominant-negative mutants of c-jun in an attempt to block c-jun dependent processes including tumor promotion and/or cellular transformation. Several mutants have been constructed including: 1) a transactivation deficient mutant with deletion between amino acid 2-122 of cJun, 2)three DNA binding mutants including one with a point mutation at position 265, a deletion at positions 269-272, and one with an insertion of 3 amino acids at position 265, 3) a dimerization dependent mutant missing the Leucine zipper. These mutants have been characterized for their ability to bind DNA and to dimerize. In addition, they have been analyzed for transactivation and transformation. The transactivation and DNA binding mutants appear to have significant ability to inhibit c-jun activity. These mutants are now ideal agents to explore and block c-jun dependent pathways. We know the transactivation mutant has the ability to inhibit phorbol ester induced tumor promotion and c-jun cellular transformation. In collaboration with Drs. Colburn, Rapp, and Bowden, we are testing these mutants in different cells systems in an attempt to block cellular transformation.